Field of the Invention
The invention relates to a gripper device in a sheet-processing machine, more particularly a sheet-fed rotary printing press, as well as to a sheet-processing machine having a gripper device. The gripper device has a gripper movable by a drive from an opened position into a closed position. The gripper is cooperatively engageable with a gripper pad associated therewith for producing a clamping force for holding sheets.
In sheet-fed rotary printing presses, the paper sheets to be printed are taken from a sheet pile and, with the aid of grippers, transported through the individual printing units of the printing press, for printing the sheets with one, two or more colors. In that regard, the grippers are mounted in a conventional manner on gripper shafts, which are disposed in a channel formed in the periphery of the respective cylinders of the printing press which transport the sheets through the machine.
In order to be able to compensate for differences in the clamping forces of the respective grippers, which can result from slight deviations or thicknesses of the grippers or the gripper pads assigned thereto relative to one another along a gripper shaft, the grippers are supported, respectively, on the gripper shaft via spring-elastic or resilient elements.
A problem resulting therefrom is that, in particular at high production-printing speeds, bouncing of the grippers can occur, leading to a disruption in the paper run or travel or to an impairment of the printed image.
Furthermore, a problem resulting with conventional sheet-fed rotary printing presses, is that, because the grippers are swivelably or pivotably mounted on the gripper shaft and, due to the swiveling or pivoting movement when the grippers are being closed, no parallel approach is attained between the clamping face of the gripper and the clamping face of the gripper pad assigned thereto. Consequently, a force component acting in the sheet longitudinal direction is formed leading to a so-called “pushing” of the grippers on the paper, which impairs the printing quality and is accompanied by increased wear.
Furthermore, in heretofore known sheet-fed rotary printing presses, there occurs a problem that the holding forces or clamping forces applied by the grippers during the operation of the printing press cannot be varied continuously and, in addition, cannot be adjusted from gripper to gripper over the width of the printing press. A resultant difficulty is that impairment of the printed image caused, for example, by one-sided pushing of the sheets because of an excessively low clamping force in one group of grippers in a row of grippers, cannot be corrected during operation. Furthermore, during the operation of the printing press, it is not possible to change over between high forces during the printing operation with inking units engaged, on the one hand, and low clamping forces during the operation without ink, on the other hand. Finally, there results likewise no possibility of adapting the clamping forces as a function of speed during the production printing operation of the printing press.
Furthermore, in the case of sheet-fed rotary printing presses of the prior art, wherein the gripper pads are not constructed so as to be vertically adjustable, the deformations of the sheet may occur in the region of the grippers, because no adaptation to the paper thickness, respectively, being processed is possible.
German Patent DE 42 00 406 C2, corresponding to U.S. Pat. No. 5,333,547, discloses, on a sheet-processing rotary printing press, a gripper device having a plurality of grippers disposed over the sheet width, which are operable by a control device via an opening and closing mechanism. The control device includes at least one measured value transmitter, a computer and at least one motor. When angular positions prescribed by the computer are reached, the grippers are operated individually and independently of one another via the associated or appertaining opening and closing mechanism driven by the motor.
European Patent EP 0 775 576 B1, corresponding to U.S. Pat. No. 5,749,572, describes a gripper control system for a cyclically oscillatingly driven pre-gripper for the individual transport of sheets in a sheet-fed rotary printing press. The pre-gripper is held at a free end of a rocking lever which is swivelable about a shaft fixed to the frame and has at least one sheet gripper. The sheet gripper is forcibly movable by cams about a joint axis aligned parallel to the rocker shaft for the purpose of closing and opening, during the sheet acceptance and sheet transfer, one of the cams rotating with a single revolution, and the other cam being swivelably mounted on a locally fixed roller lever.